BELTING LEATHER 67 



gambler, which gives a tannage which is easily curried and 

 imparts the required mellowness to the uncurried leather. 

 The great expense of this material, however, together with 

 the advent of drum stuffing and shorter tannages in stronger 

 liquors, have tended to cause a considerable reduction in 

 the proportion used for strap butts, and to limit its employ- 

 ment to the earlier stages of tanning. 



The same tendencies for reducing the time taken to 

 tan, employing stronger liquors, and securing economy of 

 labour in handling, have been evidenced in the tannage of 

 strap butts as in sole butts. It is nevertheless true that, 

 broadly speaking, strap butts receive rather more handling 

 and rather weaker liquors than sole butts. A greater amount 

 of mechanical assistance is also employed with early stages 

 (paddling, drumming, rocking). This is less objectionable 

 for curried leather than for sole butts. The handling is 

 more usually in suspension. The liquors are usually worked 

 straight down the yard as a greater mellowness is needed 

 in the early liquors than for sole butts. The offal is given 

 a separate tannage and often used for different purposes, 

 e.g. the shoulders for welting and the bellies for fancy goods. 

 Plumping with sulphuric acid is generally considered in- 

 admissible for strap butts. It has been shown that leather 

 containing sulphuric acid tends to perish after the lapse of a 

 number of years. Sole leather will be worn up before this 

 effect is observed, but belting is an article which is intended 

 to last much longer, and the use of sulphuric acid is con- 

 sequently inadvisable. Plumping must be obtained, to a 

 considerable extent, but must be achieved by the organic 

 acids (lactic, acetic, formic and butyric acids) . A few gallons 

 of such acids are consequently added to the handlers, 

 especially in the winter and spring. Less may be used in 

 the autumn, when the layer liquors which fermented in the 

 summer months have worked down to the suspenders. A 

 mixture of these acids is usually better than any one alone, 

 for they not only differ very considerably in price, but also 

 have different powers of neutralizing lime and plumping the 

 goods. Lactic acid (M.W. 90), Acetic acid (M.W. 60), and 



